1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Capacitor Conceptual Question!

  1. Jun 7, 2014 #1
    1. The problem statement, all variables and given/known data

    If you increase the charge on a parallel plate capacitor from 3μC to 9μC and increase the plate separation from 1mm to 3mm, the energy stored in the capacitor changes by a factor of...

    2. Relevant equations

    U = 1/2QV
    or 1/2CV^2

    3. The attempt at a solution

    I'm not sure which equation to even use, i'm not to great when it comes to differentiating between electric field and energy of the capacitor.

    I think I should probably use 1/2QV but i don't have a voltage to work with so i'm confused.
     
    Last edited: Jun 7, 2014
  2. jcsd
  3. Jun 7, 2014 #2
    Use the relation between charge Q, Voltage V, and Capacitance C to eliminate the voltage from the expression for the energy.
     
  4. Jun 7, 2014 #3
    so U =1/2 Q^2/C

    i'm still not sure how i would find capacitance without using the C=Q/V and not having a voltage?
    also does the distance between the plates changing not matter?
     
  5. Jun 7, 2014 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The capacitance changes if you change the distance, and you should know a formula that connects the two.
     
  6. Jun 7, 2014 #5
    oh alright i thought that the permitivity of free space had to be used when a dielectric was present only but that works thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted